This invention relates to a three-phase-enclosure type gas insulated switchgear and particularly to a three-phase-enclosure type gas insulated switchgear in which the high-voltage conductors are insulatably supported by single pedestal type support insulators.
While a pedestal type support insulator for supporting a high-voltage conductor in a three-phase-enclosure type gas insulated switchgear generally includes single pedestal types, double pedestal types, triple pedestal types, etc, the single pedestal type support insulator is advantageous in view of its compactness, the reduction in weight, lower costs and the like.
FIGS. 6 and 7 illustrate a conventional three-phase-enclosure type gas insulated switchgear as disclosed for example in Japanese U.M. Laid-Open No. 55-98117, in which three high-voltage conductors 2 are contained within a metallic vessel 1 and an electrically insulating gas 3 is filled in the metallic vessel 1. The high-voltage conductors 2 are insulatably supported by single pedestal type support insulators 4.
As seen from FIGS. 6 and 7, the high-voltage conductors 2 are disposed in parallel to extend through the apexes of a right angled equilateral triangle, and the highvoltage conductors 2 are supported by the single pedestal type support insulators 4 which extend along the central axis of the metallic vessel 1 and in the radial direction of the metallic vessel 1. Generally, the optimum direction of support of the single pedestal type support insulator 4 in the three-phase-enclsoure type gas insulated switchgear is determined by taking into consideration the mechanical performance and the electrical performance. From the view point of mechanical performance, the support direction must be selected with the shortcircuit electromagnetic force upon a shortcircuit fault taken into consideration so that the bending moment acting on the single pedestal support insulator 4 is minized. Further, from the view point of electrical performance, the support direction must be determined so that the flashover distance along the single pedestal support insulator 4 is lengthened to improve the withstand voltage characteristics.
According to experiments and analysis thereof on the shortcircuiting electromagnetic forces in a three-phase-enclosure type gas insulated bus bar conducted by the inventors of the present invention, it has been determined that the magnitude and the direction of the maximum electromagnetic force changes according to the material of the metallic vessel 1. Therefore, the optimum support direction of the single pedestal type support insulator 4 in terms of mechanical performance is different according to the material of the metallic vessel 1.
In the conventional three-phase-enclosure type gas insulated switchgear as described above, since the single pedestal type support insulators are usually mounted in the radial direction as shown in FIG. 7 irrespective of the material of the metallic vessel, the mounting of the support insulators is not optimized in accordance with the material of the metallic vessel.